Merge branch 'temp-upstream-rebrand' into main

Resolves merge conflicts:
- install.sh, build.sh, .github/workflows/build.yml: Reverted to Dushnilin's versions to avoid installing SourceForge mirrors.
- fe-app-tachyon: Resolved type, formatting and copyOutbound conflicts, keeping both Dushnilin's custom features and ushan0v's frontend performance optimizations.
- backend: Kept Dushnilin's ucode refactorings, Telegram bot integration, and release repository URL (Dushnilin/tachyon) while merging updates.uc cache format v8 & persistent cache format v7.
- tests: Merged tests from both branches, preserving ucode -L wrappers for local test execution.

.github/workflows/backend-ci.yml

@@ -7,6 +7,7 @@ on:
       - 'tachyon/Makefile'
       - 'build.sh'
       - 'tests/**'
+      - '.github/workflows/build.yml'
       - '.github/workflows/backend-ci.yml'
   push:
     branches:
@@ -16,6 +17,7 @@ on:
       - 'tachyon/Makefile'
       - 'build.sh'
       - 'tests/**'
+      - '.github/workflows/build.yml'
       - '.github/workflows/backend-ci.yml'
 
 jobs:
@@ -54,8 +56,4 @@ jobs:
       - name: Run backend tests
         shell: bash
         run: |
-          for test_script in tests/*.sh; do
-            echo "::group::$test_script"
-            bash "$test_script"
-            echo "::endgroup::"
-          done
+          printf '%s\0' tests/*.sh | xargs -0 -n1 -P4 bash